1. Field of the Invention
The present invention relates to a method of reducing a nitrile into a corresponding alcohol and, more particularly, to a new and useful method of causing a nitrile to react with an alcohol in the presence of a catalyst, to obtain a desired alcohol.
2. Description of the Prior Art
Various conventional methods of reducing nitriles are known to those skilled in the art. A first conventional method is reduction by a hydride compound such as lithium aluminium hydride or aluminium hydride. A second conventional method s reduction of nitrile with an alkali metal such as lithium, sodium, or calcium in aqueous ammonia or an amine solvent. A third conventional method is electrolytic reduction, and a fourth is reduction by catalytic hydrogenation, using a heterogeneous catalyst.
When nitriles are reduced according to the above methods, the primary products produced are generally amines or, in special cases, aldehydes. The amine is converted into an alcohol via diazotation, while the aldehyde can be reduced and converted into an alcohol by sodium borohydride or the like, ("Shin Jikken Kagaku Kouza" Vols. 14 and 15, Maruzen).
Meerwein-Ponndorf-Verley reduction is a known reducing method which uses an inexpensive alcohol such as isopropanol as a hydride source. However, the purpose of this method is known to derive an alcohol from an aldehyde or ketone, not to reduce a nitrile (A. L. Wilds, Org. React., 2, 178, 1944).
The above conventional methods present the following problems.
According to the first method, expensive hydride compounds such as lithium aluminium hydride and aluminium hydride must be used. These hydride compounds are highly reactive with water, and thus care must be taken in their storing and handling. In addition, the reactivity is too strong, and produce highly flammable hydrogen gas.
According to the second method, an active metal, i.e., an alkali metal (e.g., lithium or sodium) or an alkaline earth metal (e.g., calcium) is used. These active metals, however react vigorously with water, giving rise to spontaneous ignition, and so are difficult to handle. Further, in order to obtain the reaction product, the non-reacted metal must be deactivated with water, and extraction carried out using an organic solvent, thus necessitating cumbersome and time-consuming operations.
According to the third method, an apparatus specifically designed for electrolysis must be employed. This method is therefore not economical.
According to the fourth method, i.e, reduction over heterogeneous catalytic hydrogenation, care must be taken, as hydrogen gas is used.
According to the above conventional methods, desired alcohols cannot be primarily obtained. As described above, the primary products in the above methods are mainly amines or, in special cases, aldehydes. In order to derive alcohols from amines or aldehydes, additional steps is required. In general, a reaction for diazotating amines to obtain alcohols produces a low yield. In particular, when a primary amine is used, the reaction involves isomerization, and a primary alcohol cannot be obtained generally. Use of sodium borohydride, to reduce an aldehyde into an alcohol, is expensive and care must be taken in its handling.